As wireless networks become increasingly popular, there is growing demand for efficient systems supporting quality of service (Qos) requirements that allow for different types of services to be provided for a variety of communications needs. In addition, such systems may need to provide both centrally-controlled as well as distributed modes of operation while continuing to support Qos requirements. The resulting increase in the complexity of these systems tends to cause increased latency and other effects that can significantly impair performance, especially as network congestion grows.
FIG. 1 depicts an illustrative wireless network 100. As shown, wireless network 100 includes an access point (AP) 102 and stations (STAs) 104 and 106. Typically, wireless networks may include numerous APs and STAs, but the simplified wireless network 100 is depicted here for illustrative purposes. Wireless network 100 represents a flexible system that supports Qos requirements while allowing for both centrally-controlled as well as distributed modes of operation. For example, wireless network 100 may allow eight different types of service, represented by eight different traffic categories (TCs), while operating using either a hybrid coordination function (HCF) or an enhanced distributed coordination function (EDCF). Generally speaking, a system operating in HCF mode may use a central node to control transmissions amongst a plurality of nodes during contention free periods (CFPs). Each node that wishes to send out a transmission must first send a request for a transmission opportunity (TXOP) to the central node. The central node allocates the channel by polling selected nodes. The central node polls each selected node by sending to it a poll transmission identifying a particular TXOP defined for a specific time and duration. A polled node may then send its queued transmission during the granted TXOP. Because there may be eight TCs, each node may maintain eight different queues of transmissions awaiting TXOPs. Correspondingly, the central node may need to keep track of information, such as queue size, relating to each of the eight queues, for each of the nodes controlled by the central node. At the same time, the central node may need to decide which nodes are to be polled and also send out the corresponding poll transmissions. The central node must accomplish all this in within tightly control time limits, since each selected node must be polled in time for it to react and send out its queued transmission within the granted TXOP. The central node itself may request and grant to itself a TXOP during which it may send its own transmissions to one or more other nodes. An AP such as AP 102 may serve as the central node. STAs such as STA 104 and 106 may represent other nodes that may send out transmissions by first requesting a TXOP from AP 102 and then transmitting during allocated TXOPs when polled by AP 102.
The complex and time sensitive processing and transmission operations that must be performed by a node in a wireless network such as wireless network 100 present a formidable challenge in hardware and software design. For example, any latency in the processing and sending of polls may significantly undermine performance by creating delays in the transmission of polls, which can in turn increase the likelihood that polled nodes may not have sufficient time to perform their transmission within the allotted TXOPs. This may lead to wasted TXOPs that degrade the overall throughput performance of the wireless network, particularly when the wireless network experiences congestion. Thus, there is a urgent need for improving the latency characteristics of nodes that participate in wireless networks as complexity and congestion increases.